As shown by Banucci et al U.S. Pat. No. 4,098,800, assigned to the same assignee as the present invention, particulated oligomeric polyetherimide acids can be made by effecting reaction between (a) an aromatic bis(ether anhydride) or "organic dianhydride" of the formula, ##STR1## and (b) mixtures of one or more of said bis(ether anhydride)s with up to 30 mole percent benzophenone dianhydride of the formula, ##STR2## with at least one organic diamine of the general formula, EQU H.sub.2 N--R--NH.sub.2, (3)
in an inert organic liquid selected from the group consisting of (c) chlorinated hydrocarbon selected from the group consisting of methylene chloride, chloroform, 1,2-dichloroethane, and mixtures thereof and (d) mixtures of said chlorinated hydrocarbon with up to 50% by weight of acetone to form oligomeric polyetheramide-acid which is substantially insoluble in said liquid, where Z is a member selected from ##STR3## and divalent organic radicals of the general formula, ##STR4## where X is a member selected from the class consisting of divalent radicals of the formulas, ##STR5## where y is an integer from 1 to 5, and R is a divalent organic radical selected from the class consisting of aromatic hydrocarbon radicals having from 6 to about 20 carbon atoms and halogenated derivatives thereof, alkylene radicals having from 2 to about 20 carbon atoms, cycloalkylene radicals having from 3 to about 20 carbon atoms, from C.sub.2 to about C.sub.8 alkylene terminated polydiorganosiloxane and divalent radicals of the formula, ##STR6## where Q is a member selected from --O--, --S--, and --C.sub.x H.sub.2x --, x is is an integer from 1 to 5 and a is 0 or 1.
It has been found that the above-described particulated polyetheramide acids of Banucci et al are useful in various coating applications, for example, applications to aluminum or copper wire using fluid bed electrostatic coating procedures. However, these electrostatically applied oligomeric powders often form films containing entrapped bubbles which reduces the utility of the resulting polyetherimide as an insulating coating.
In copending application RD-8287, filed concurrently herewith, improved results were achieved when the particulated, substantially organic solvent-free polyetheramide acid of Banucci et al was heated in a non-oxidizing atmosphere for a time sufficient to effect at least a 70% imidization without substantially sintering the powder. A reduction in bubbling of films was achieved when the imidized powder was applied onto various substrates such as wire. However, the resulting films were often highly cross-linked, or the polyetheramide acid oligomers often had amine terminal groups rendering the prepolymers unsuitable for making high molecular weight thermoplastics by standard injection molding techniques.
The present invention is based on the discovery that particulated substantially organic solvent-free polyetherimide oligomer, capable of being injection molded to the high molecular weight state, can be made by coreacting substantially equal molar amounts of aromatic bis(etheranhydride) of formula (1) and organic diamine of formula (2) under aqueous interfacial polymerization conditions, instead of using a halogenated organic solvent in the absence of water as utilized by Banucci et al. The surprising feature of the present invention, is that the use of water in combination with an appropriate organic solvent under interfacial polymerization conditions has been found to allow for the recovery of a polyetheramide acid product in which the stoichiometry of the initial aromatic bis(ether anhydride) and organic diamine reactants is substantially maintained. As a result, the recovered polyetheramide acid can be readily converted to a high molecular weight injection moldable plastic substantially free of cross-linking.